refactor(controller,xceadmin): drop generic Resource.unit, hardcode bytes for maxmem

Simplification per review feedback on e3b3ffa: a generic schema-driven
unit field touched the capnp wire schema (2 structs), C structs
(xce_resource_t/xce_resval_t), resobj.c's deep-copy/destroy, opget.c's
reply-build lookup, resources.yaml/resources.schema.json, and mapping.py
-- real cross-cutting cost for a mechanism only one resource (maxmem)
actually needs today.

Reverted all of that. The controller CLI (test.c) now just knows
"maxmem" is bytes-valued via a small explicit is_bytes_valued_resource()
name list, and adaptively picks the best-fit human unit at display time
(format_bytes_human, unchanged) -- same observable behavior (resval/
workerlist render maxmem as e.g. "30.90 GB"), zero wire schema surface.
Regenerated the xceadmin golden fixture back to its pre-unit-field size
(5304 bytes, exactly matching the size right after the mxj-only fix,
confirming a clean, complete removal).

Verified: 1095/1095 controller_unit_test (3 runs; one hit the
pre-existing flaky segfault already logged as bug-1553, unrelated),
228/228 xceadmin pytest, clean rebuild of lib/controller/xceadmin/xce_test.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/include/xce/types.h

@@ -49,7 +49,6 @@ typedef struct {
     char*      name;
     char*      host;
     xce_val_t* val;
-    char*      unit;
 } xce_resval_t;
 
 typedef struct {
@@ -143,7 +142,6 @@ typedef struct {
     int                  ndistributions;
     res_distribution_t** distributions;
     xce_val_t*           hbased_defined;
-    char*                unit;
 } xce_resource_t;
 
 typedef struct {